1. Field of the Invention
The present invention relates to a semiconductor heat-treating apparatus, particularly an impurity diffuser.
2. Description of the Prior Art
So far is known vertical type diffusers as apparatus for subjecting semiconductor wafers to impurity diffusing treatment. Such a prior art diffuser is illustrated in FIGS. 1 and 2, which has a diffusing furnace 9 consisting of a furnace-core tube 1 (referred to as core tube hereinafter) and an electric furnace 2 for heating the core tube. A number of semiconductor substrates 3 are loaded on a boat 4 supported by a shaft 5 and carried into or out of the furnace-core tube. Besides, there is provided a box-shaped scavenger 6 surrounding the upper-opening 10 of the core tube 1 through which the semiconductors are carried into or out. The scavenger 6 has on one side an outlet 7 for discharging air, reaction gas and diffusion gas 11 and on the other side apertures 8 for allowing air 12 to flow in.
In the apparatus, the wall of scavenger 6 receives radiant energy from the heater 2 extending to the vicinity of the core tube opening 10, becomes temperature-elevated. When semiconductor substrates 3 are carried into the furnace 9 through the scavenger 6, they are heated by the temperature-elevated wall and exposed to air from the outside air. When they are being carried into core tube 1, undesirable air such as air 13 present between semiconductor substrates arrayed and entrained outside air 13 are introduced into the interface between the semiconductor substrate 3 and oxide film on the surface thereof, with the result of formation of film of incomplete combination with oxygen, accompanied by increase in the interfacial charge density resulting from the incomplete oxidation. In addition to the deterioration of semiconductor element properties, there is problem with contamination of outside air.